284 Journal New York Entomological Society. [VoLXXIv. 



Summary. 



The principal points brought out in the preceding discussion may- 

 be briefly summarized as follows. Crustacea (c. g., Bathynella, 

 Anaspides, Ligia, etc.) " Myriopoda " {Scolopendrella, Scutigera, 

 etc.) and the lower insects {e. g., Eosentomon, Anajapyx, Machilis) 

 form the three apices of a triangle, each apex of which is connected 

 with the other two by mutual bonds of relationship. These three 

 groups are related to the Trilobita (such as Triarthrus, etc.), and 

 through the Trilobites they are rather distantly related to Limulus 

 and the Arachnids, but the Arachnid line of development diverges 

 markedly from that of the three groups mentioned above as shown 

 in fig. 2. The ancestors of Arthropods in general, were doubtless 

 related to Annelidan worms and to Peripatus. 



The Apterygota have retained characters suggestive of both 

 Crustacean and Myriopodan affinities, and some of the Apterygotan 

 lines of development are nearer to the Crustacea than to the 

 " Myriopoda " in certain respects, while others are clearly much 

 nearer to the " Myriopoda." The Apterygota as a whole doubtless 

 arose from ancestors occupying a position intermediate between the 

 Crustacean and " Myriopodan " lines of descent, as shown in the 

 diagram, fig. 2). The Apterygota are much more primitive than their 

 nearest Pterygotan relatives (the Blattids, Plecoptera and Epheme- 

 rids) and have departed the least from the probable ancestral condi- 

 tion of the Hexapoda, despite Handlirsch's contention to the contrary. 



There are three main lines of development (possibly only two) in 

 the Apterygota. These consist of the insects grouping themselves 

 about the Protura, Rhabdura, and Thysanura, and they are divided 

 into three sections termed the Proturadelphia, Rhabduradelphia, and 

 Thysanuradelphia. The first group constitutes the non-styli-bearing 

 Apterygota (Astyligera), while the last two constitute the styli-bear- 

 ing Apterygota (Eustyligera). These may be further divided into 

 seven or more orders represented by the Dasyleptidse ( ?), Machilidae, 

 Lepismatidse, Campodeidse, Japygidse, Eosentomidse, and Entomo- 

 bryidse (with the Sminthuridse ?). 



As a whole, the Eosentomid group is the most primitive. The 

 Entomobryids, Sminthurids, etc., are rather closely related to the 

 Protura, but represent more or less degenerate offshoots which 



